Staplers are an indispensable part of office appliances for fastening papers or documents. Conventionally, depending on the thickness of a set of paper sheets, an operator chooses different commercially available stapling machines and/or sizes of staples to accommodate the need. For example, a heavy duty stapler with long leg staples is used for attaching a relatively large number of sheets of paper, and a hand held desk stapler equipped with short leg staples is utilized for a relatively small number of sheets of paper. Hence, the operator must purchase and maintain at least two kinds of staplers in his office for these different uses. This is neither convenient, nor economical, particularly for a company that has a large number of personnel.
In an attempt to remedy this problem, the prior art provides a single stapler loaded with standard size staples having relatively long legs in order to try to join sets of paper sheets having different thicknesses. Although this compromise may prove to be economically successful, it does not produce the desired stapling quality. When such a stapler is used to produce a set containing only two or three sheets of paper, the staple re-penetrates through the paper sheets during the stapling operation. Because of the relatively long legs of the staples, the staple legs protrude outwardly from the top sheet of the set. The stapling operation not only yields a very unsightly stapled set, but the exposed legs can puncture the operator's fingers when stapled documents are handled. On the other hand, when a set of a large number of sheets of paper are to be stapled, the staple can collapse at its bridge portion to form a "M" shape during the stapling operation due to the increased resistance generated from the thicker set of paper sheets.
In the prior art, U.S. Pat. 4,315,589 issued to Soong discloses a stapling apparatus which improves stapling capability in handling thin sets of sheets, say on the order of two or three sheets, as well as thick sets, on the order of 20 or more sheets. To achieve its objective, the stapling apparatus uses an anvil to bend the staples during the driving operation by the driver member. The anvil is formed with a depression or opening between the staple clinching grooves and is of a size which includes the adjacent ends of the grooves. The clinching grooves have their longitudinal axes parallel but at an angle relative to the bridge portion of the staple to prevent the legs of the staple from interfering with each other during the stapling operation. The depression or opening between the clinching grooves assists in controlling operation to prevent re-entry or re-penetration of the legs through the top sheet when a stack of sheets is being stapled.
Although the stapling apparatus of this patent can improve the stapling quality for a thin set of paper sheets, it is still unable to be used as a hand held device for stapling a thick set of paper sheets, such as, e.g., 50-60 sheets. This is because the device does not provide sufficient leverage for proper penetration of the sheets. Also, the staple can collapse during stapling of a thick set of sheets.
Moreover, there is no commercially available hand held heavy duty stapler which is capable of stapling a set of paper from 2 to 60 sheets. In the prior art, a table top heavy duty stapler is used to staple a thick set of paper sheets. An operator uses one hand to grasp a driving arm to press it down and effect the stapling operation. In other words, prior art heavy duty staplers are not hand held and are not operated unless the stapler is placed on a table or other flat support surface so that the used can apply sufficient leverage to the handle to penetrate the sheets with the staple. Otherwise, it is difficult, if not impossible, for a user to grasp the stapler and operate it like a personal stapler adapted for joining thin sets of paper sheets.
Thus, there remains a need for a single device that can successfully staple various sets of paper sheets ranging from only a few sheets to as many as 50 or 60. Furthermore, it would be advantageous for such a device to be operable as a convenient, hand held device. The present invention provides one such device.